Image display apparatus capable of displaying personal computer signals and television signal by conversion into a signal of a higher number of pixels

ABSTRACT

The present invention aims at providing an image display apparatus capable of displaying both a television signal and an image signal supplied from a personal computer with a high picture quality on a high definition display unit having 1024 by 768 pixels. In order to achieve this object, an image display apparatus according to the present invention includes an NTSC-VGA conversion circuit for converting a television signal to a signal having 640 by 480 pixels and corresponding to the non-interlacing VGA standard, a switch unit for selecting and outputting either the signal outputted from the NTSC-VGA conversion circuit and an inputted image signal from a personal computer, and a VGA-XGA conversion circuit for converting a number of pixels of a signal outputted from the switch unit to a number of pixels 1024 by 768 substantially equivalent to the number of the display unit.

BACKGROUND OF THE INVENTION

The present invention relates to an image display apparatus capable ofdisplaying images in common for image information signals of differentsignal forms supplied from various different image sources such astelevision signals and image signals supplied from personal computers.

In recent years, attention is paid to image display apparatuses ofso-called multimedia type adapted to be able to display imageinformation signals supplied from different image sources such astelevision signals and signals supplied from personal computers.

In an example thereof, it is attempted to display an image supplied froma personal computer on a television set widely spread in ordinary homes.When this television set corresponds to the NTSC system in this case, animage information signal from the personal computer is converted intovideo signals of the NTSC system and then supplied to the televisionset. A system in which image an information signal fed from a personalcomputer is supplied to a television set to display the images thereonis described in JP-A-7-123368, for example.

In another example, a received television program is displayed on adisplay apparatus dedicated to a personal computer.

SUMMARY OF THE INVENTION

In the case where images supplied from a personal computer are displayedon a television set, the picture quality of the displayed images isrestricted by the number of pixels of the television set. In the case ofa television set of the NTSC system, one frame has two fields and aninterlacing system of 2:1 is adopted. The number of pixels on the screenof one frame is 640 (horizontal) by 480 (vertical). As for the outputimage information signal of the personal computers, there are differentsignal forms, such as the non-interlacing VGA signal form with 640 by480 pixels, the SVGA form with 800 by 600 pixels, and the XGA form with1024 by 768 pixels. Therefore, when an image signal supplied from apersonal computer corresponding to the SVGA or the XGA form is displayedon a television set of the NTSC system, the picture quality issignificantly degraded and the original high picture quality is notexhibited.

An object of the present invention is to provide an image displayapparatus free from the above described problem and capable ofdisplaying images supplied from an image source with a high picturequality irrespective of the kind (i.e., the signal form of the imageinformation signal) of the image source.

In accordance with the present invention, the above described object isachieved by using a display unit having a larger number of pixels thanthe input image information signal, converting the input imageinformation signal to a signal having a signal form associated with thedisplay unit, and displaying a resultant image on the display unit.

Specifically, in accordance with the present invention, an image displayapparatus receiving a first image information signal and a second imageinformation signal having a larger number of pixels per screen than thefirst image information signal and capable of displaying an image foreach of the first and second image information signals includes adisplay unit having a number of pixels larger than the number of pixelsof the second image information signal, a first signal conversioncircuit for converting the number of pixels of the first imageinformation signal to a number of pixels substantially equivalent to thenumber of pixels of the second image information signal, a switch unitfor selecting and outputting either the image information signalconverted in number of pixels by the first signal converson circuit orthe inputted second image information signal, and a second signalconversion circuit for converting a number of pixels of an imageinformation signal outputted from the switch unit to a number of pixelssubstantially equivalent to the number of the display unit.

More specifically, in accordance with the present invention, an imagedisplay apparatus receiving as inputs a television signal of the NTSCsystem and an image information signal having 640 by 480 pixels andcorresponding to the non-interlacing VGA standard outputted from apersonal computer and capable of displaying an image for each of thetelevision signal and the image information signal includes a displayunit having 1024 by 768 pixels and corresponding to the non-interlacingXGA standard, an NTSC-VGA conversion circuit for converting thetelevision signal to a signal having 640 by 480 pixels and correspondingto the non-interlacing VGA standard, a switch unit for selecting andoutputting either the signal outputted from the NTSC-VGA conversioncircuit and the inputted image information signal, and a VGA-XGAconversion circuit for converting a number of pixels of a signaloutputted from the switch unit to a number of pixels 1024 by 768substantially equivalent to the number of the display unit.

As a result, the television signal and the image information signalsupplied from the personal computer can be displayed on the display unitwith a number of pixels nearly equal to the number of pixels possessedby the display unit. For each image information signal, an image with ahigh picture quality is thus obtained.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram showing an implementation form of an imagedisplay apparatus according to the present invention;

FIG. 2 is a block diagram showing a concrete example of an NTSC-VGAconversion circuit illustrated in FIG. 1;

FIGS. 3A and 3B are block diagrams showing a concrete example of amotion adaptive scanning line interpolation circuit included in thesignal conversion circuit illustrated in FIG. 2;

FIG. 4 is a block diagram showing a concrete example of a VGA-XGAconversion circuit illustrated in FIG. 1;

FIGS. 5A through 5C are schematic diagrams showing operation in theconcrete example of the VGA-XGA conversion circuit illustrated in FIG.4; and

FIGS. 6A and 6B are diagrams showing operation for converting the numberof pixels by using gradation integral in the concrete example of theVGA-XGA conversion circuit illustrated in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, implementation forms of the present invention will bedescribed by referring to the drawing. FIG. 1 is a block diagram showingan implementation form of an image display apparatus according to thepresent invention. Numerals 1 and 2 denote input terminals. Numeral 3denotes a channel tuning unit, and numeral 4 denotes an NTSC-VGAconversion circuit. Numeral 5 denotes a changeover switch, and numeral 6denotes a VGA-XGA conversion circuit. Numeral 7 denotes a display unit.

In FIG. 1, the display unit 7 is a TFT liquid crystal panel or acathode-ray tube, for example. The display unit 7 is a display unithaving a larger number of pixels than that corresponding to the NTSCsystem and capable of displaying images with a high picture quality,such as a TFT liquid crystal panel corresponding to the XGA. It is nowassumed that the display unit 7 is a display unit conforming to the XGAform with 1024 by 768 pixels.

From the input terminal 1, broadcast television signals of respectivechannels are inputted. The broadcast television signal of a desiredchannel is selected by the channel tuning unit 3. It is now assumed thatthis broadcast television signal is a television signal of the NTSCsystem which is one of standard television systems (a composite signalwith the 2:1 interlacing of 525/30 and a horizontal frequency of 15.734kHz which is hereafter referred to as NTSC signal).

The NTSC signal of the desired channel outputted from the channel tuningunit 3 is supplied to the NTSC-VGA conversion circuit 4 for convertingthe signal form and converted to a video signal of the VGA form withnon-interlacing of 525/60 and a horizontal frequency of 31.5 kHz whichis twice that of the NTSC system.

On the other hand, an image information signal having a signal form VGA,SVGA or XGA is inputted from a personal computer which is notillustrated via the input terminal 2. The changeover switch 5 iscontrolled to be changed over under a user's instruction. Either theoutput image information signal supplied from the personal computer viathe input terminal 2 or the video signal of the VGA form supplied fromthe NTSC-VGA conversion circuit 4 can be selected by the changeoverswitch 5.

The output image information signal of the personal computer or thevideo signal of the VGA form selected by the changeover switch 5(hereafter generally referred to as image information signal) issupplied to the VGA-XGA conversion circuit 6 for converting the signalform. In the case where the supplied image information signal has asignal form other than the XGA, such as the VGA or SVGA, the signal isconverted to an image information signal of the XGA form by the VGA-XGAconversion circuit 6 and then supplied to the display unit 7. In thecase where the supplied image information signal is an image informationsignal of the XGA form, it is supplied to the display unit 7 as it is.Both the video image of the television signal of the NTSC systemreceived by the channel tuning unit 3 and the image of the output imageinformation signal of the personal computer of the VGA form or the SVGAform inputted from the input terminal 2 are displayed with the number ofpixels (1024 by 768) conforming to the display unit 7 corresponding tothe XGA. The image of the output image information signal of a personalcomputer corresponding to the XGA inputted from the input terminal 2 isalso displayed in the same way. Therefore, any of these images isdisplayed with a possible picture quality in the display unit 7.

FIG. 2 is a block diagram showing a concrete example of the NTSC-VGAconversion circuit illustrated in FIG. 1. Numeral 8 denotes an inputterminal. Numeral 9 denotes a signal processing circuit including athree-dimensional Y/C separation circuit, a color demodulation circuit,and a color adjustment circuit. Numeral 10 denotes a field memory.Numeral 11 denotes a signal conversion circuit including a motionadaptive scanning line interpolation circuit and an RGB conversioncircuit. Numeral 12 denotes a field memory, and 13R, 13G and 13B denoteline memories for double rate conversion. Numeral 14 denotes a D/Aconversion circuit. Numeral 15 denotes a system controller.

In FIG. 2, the above described NTSC signal inputted from the inputterminal 8 is supplied to the signal processing circuit 9. In thissignal processing circuit 9, this NTSC signal is converted to a digitalsignal and then separated into a luminance signal and a carrierchrominance signal by the three-dimensional Y/C separation circuit byusing the field memory 10. This carrier chrominance signal isdemodulated to chromaticity signals I and Q by the color demodulationcircuit. In this case, these chromaticity signals I and Q are controlledby the system controller 15. Thereby, the hue and the color density areadjusted.

The luminance signal Y and the chromaticity signals I and Q outputtedfrom the signal processing circuit 9 are supplied to the signalconversion circuit 11. In conjunction with the line memories for doublerate conversion 13R, 13G and 13B, the signal conversion circuit 11generates primary color signals R, G and B corresponding to the VGA fromthe luminance signal Y and the chromaticity signals I and Q of the NTSCsystem.

In order to generate interpolation horizontal scanning lines forachieving the 520/60 non-interlacing for each of the luminance signal Yand the chromaticity signals I and Q, interfield interpolationprocessing is conducted while incorporating the detected motion value bythe motion adaptive scanning line interpolation circuit in the signalconversion circuit 11 by using the field memory 12. For each of theoriginal horizontal scanning lines and the generated interpolationhorizontal scanning line, the luminance signal Y and the chromaticitysignals I and Q are subjected to computation processing to generate theprimary color signals R, G and B. These primary color signals R, G and Bare respectively written into the line memories 13R, 13G and 13B fordouble rate conversion in the order of sequenced horizontal scanninglines (including the interpolation horizontal scanning lines). Theprimary color signals are read out with a rate which is twice that ofwriting. Each horizontal scanning line is thus compressed on time axisas compared with the NTSC system.

As described above, the above described signal of each of the inputtedhorizontal scanning lines is used for interfield interpolationprocessing. In addition, the signal of each of the inputted horizontalscanning lines is temporarily written into the field memory 12. Thesignals of the interpolation horizontal scanning lines generated asdescribed above are also written into the field memory 12. Thesehorizontal scanning lines (including the interpolation horizontalscanning lines) are read out from the field memory 12 in the orderrequired for screen configuration and supplied to the line memories fordouble rate conversion 13R, 13G and 13B. Each of the line memories fordouble rate conversion 13R, 13G and 13B has two line memories(provisionally referred to as A and B). If the primary signalscorresponding to one horizontal scanning line are written into the linememories A and B, they are read out with a rate equivalent to twice thatof writing. The write operation of the line memories A and B is deviatedfrom the read operation by a period of time equivalent to half of onehorizontal scanning period of the written primary signals. From the linememory 13R for double rate conversion, therefore, the primary signal Rof each horizontal scanning line compressed to a half on time axis isobtained continuously. As for the line memories 13G and 13B for doublerate conversion, the same holds true.

The primary signals R, G and B compressed on time axis and outputtedfrom the line memories for double rate conversion 13R, 13G and 13B areconverted to analog signals by the D/A conversion circuit 14. As aresult, the primary signals R, G and B of 525/60 non-interlacing with aperiod of horizontal scanning line equivalent to 31.5 kHz are obtained.They are component signals of the VGA form having 640 by 480 pixels.

In the signal conversion circuit 11, a synchronization signal isseparated from the inputted luminance signal Y. From this separatedsynchronization signal, a non-interlacing vertical synchronizationsignal V of 60 Hz and a horizontal synchronization signal H of 31.5 kHzsynchronized to the component signal of the VGA form are generated.

FIG. 3A is a block diagram showing a concrete example of the motionadaptive scanning line interpolation circuit in the signal conversioncircuit 11 illustrated in FIG. 2 by taking the luminance signal Y as anexample. Numeral 16 denotes an input terminal. Numeral 17 denotes aninterfield interpolation circuit, and numeral 18 denotes an interlineinterpolation circuit. Numeral 19 denotes a motion detection circuit,and numeral 20 denotes a mixing circuit. Numeral 21 denotes an outputterminal.

FIG. 3B is a diagram showing the operation of this concrete example.

With reference to FIG. 3A, the output luminance signal Y supplied fromthe signal processing circuit 9 (FIG. 2) is inputted via the inputterminal 16 and supplied to the interfield interpolation circuit 17, theinterline interpolation circuit 18, and the motion detection circuit 19.The motion detection circuit detects a motion portion of the video imageand its speed from the input luminance signal Y. According to a resultof this detection, the motion detection circuit controls the mixingcircuit 20 to change a mixing ratio between the output luminance signalof the interfield interpolation circuit 17 and the output luminancesignal o the interline interpolation circuit 18. In still portions ofthe video image, only the output luminance signal of the interfieldinterpolation circuit is passed through the mixing circuit 20. In amotion portion of the video image, the mixing ratio of the outputluminance signal of the interline interpolation circuit 18 becomeslarger as the motion becomes faster.

In the case of interlacing of 2:1, it is now assumed that horizontalscanning lines of the N-th field N are A, B, C, . . . in the order andhorizontal scanning lines of the (N+1)-th field (N+1) are A', B', C', .. . in the order as shown in FIG. 3B. Then on the screen, the horizontalscanning line A' is displayed between the horizontal scanning lines Aand B. The horizontal scanning line B' is displayed between thehorizontal scanning lines B and C.

Every two consecutive fields N and N+1, the interfield interpolationcircuit 17 uses, as interpolation horizontal scanning lines between twoadjacent horizontal scanning lines of the preceding field N, horizontalscanning lines of the succeeding field (N+1) to be displayed between thehorizontal scanning lines by means of interlacing. As interpolationhorizontal scanning lines between the horizontal scanning lines A and B,between the horizontal scanning lines B and C, . . . of the field N, thehorizontal scanning lines A', B', . . . of the next field (N+1) are usedin FIG. 3B. Owing to the interpolation processing in the still portion,a high resolution can be maintained in this portion at the time ofconversion from interlacing to non-interlacing without impairing thecontour portion.

The interline interpolation circuit 18 functions to generate signals ofinterpolation horizontal scanning lines in the field. By taking thefield N as an example in FIG. 3B, the signal of the interpolationhorizontal scanning line between the horizontal scanning lines A and Bis derived from the horizontal scanning lines A and B as, for example,the average (A+B)/2 of successive pixels of the signals of thehorizontal scanning lines A and B. In the motion portion, contents ofimages differ from field to field. Therefore, video images with smoothmotion are obtained by effecting interline interpolation rather than theinterfield interpolation.

In the NTSC-VGA conversion circuit 4 illustrated in FIG. 2, conversionfrom the NTSC system to the VGA form can be conducted without impairingthe picture quality as heretofore described.

FIG. 4 is a block diagram showing a concrete example of the VGA-XGAconversion circuit illustrated in FIG. 1. In FIG. 4, 22R 22G and 22Bdenote A/D conversion circuits and 23R, 23G and 23B denote horizontalfrequency conversion circuits. Furthermore, 24R, 24G and 24B denote linememories and 25R, 25G and 25B denote pixel number conversion circuits.Numeral 26 denotes a microcomputer. Numeral 27 denotes a PLL(phase-locked loop).

With reference to FIG. 4, the primary color signals R, G and B fed fromthe changeover switch 5 (FIG. 1) are supplied respectively to the A/Dconversion circuits 22R 22G and 22B and converted to digital signals byusing a clock supplied from the PLL 27. This PLL operates in synchronismwith a horizontal synchronizing signal H supplied together with theprimary color signals R, G and B. Therefore, the PLL 27 is controlled bythe microcomputer 26 depending upon the signal form of the inputtedprimary color signals R, G and B such as the VGA form, the SVGA form orthe XGA form.

Subsequent processing is the same for the primary color signals R, G andB. Therefore, processing for the primary color signal R will behereafter described.

A digital primary color signal R outputted from the A/D conversioncircuit 22R is converted to a primary color signal R having a horizontalfrequency of the XGA type by a horizontal frequency conversion circuit23R. The horizontal frequency conversion circuit 23R includes linememories, for example. Although not illustrated, its writing isconducted with a rate according to the output clock of the PLL 27. Itsreading is conducted according to the clock corresponding to the XGA.Therefore, the horizontal frequency is converted in the horizontalfrequency conversion circuit 23R in the case where the video signal ofthe VGA form converted by the NTSC-VGA conversion circuit 4 (FIG. 1) oran output image information signal of a personal computer having asignal form other than the XGA such as the VGA or SVGA is inputted.However, conversion of the horizontal frequency is not conducted in thecase where an output image information signal of a personal computerhaving the XGA form is inputted.

If the horizontal frequency in the VGA form (31.5 kHz) is converted tothe horizontal frequency in the XGA form (48.4 kHz), the horizontalscanning lines are compressed on the time axis by approximately 2/3times. If the horizontal frequency in the SVGA form (37.9 kHz) isconverted to the horizontal frequency in the XGA form, the horizontalscanning lines are compressed on the time axis by approximately 4/5times.

The primary color signal R outputted from the horizontal frequencyconversion circuit 23R is supplied to the display controller 25R. Inaddition, the primary color signal R outputted from the horizontalfrequency conversion circuit 23R is delayed in the line memory 24R byone horizontal period of the image information signal of the XGA formand supplied to the display controller 25R. Th s display controller 25Rfunctions to convert the number of pixels to that (1024 by 768) of theXGA form by using the primary color signal R supplied from thehorizontal frequency conversion circuit 23R and the primary color signalR supplied from the line memory 24R. The primary color signal Rprocessed by this display controller 25R is supplied to the display unit7 illustrated in FIG. 1.

Assuming now that the primary color signal R inputted to the A/Dconversion circuit 22R has the VGA form (640 by 480), each of the numberof horizontal pixels and the number of vertical pixels is increased to1.5 times to generate a primary color signal R close to the XGA form asshown in FIG. 5A. With respect to the primary color signal R suppliedfrom the horizontal frequency conversion circuit 23R, two horizontalscanning lines are converted to three horizontal scanning lines by usingthe primary color signal R supplied from the horizontal frequencyconversion circuit 23R. Furthermore, in each horizontal scanning line,two pixels are converted to three pixels.

For converting two horizontal scanning lines to three horizontalscanning lines, it is necessary to form an interpolation horizontalscanning line between the two horizontal scanning lines on the basis ofthe two scanning lines. It is now assumed that an output horizontalscanning line of the line memory 24R is LA and a horizontal scanningline outputted from the horizontal frequency conversion circuit 23Rsimultaneously with the LA is LB. (These horizontal scanning lines LAand LB are adjacent horizontal scanning lines before conversion. Thehorizontal scanning line LA precedes the horizontal scanning line LB.)The average of the primary color signal R between LA and LB is used asthe primary color signal R of an interpolation horizontal scanning lineLAB. Subsequently to the horizontal scanning line LA, this interpolationhorizontal scanning line LAB is disposed. Subsequently to theinterpolation horizontal scanning line LAB, the next horizontal scanningline LC supplied from the line memory 24R is disposed. As a matter ofcourse, this horizontal scanning line LC is used to form the nextinterpolation horizontal scanning line.

Conversion of two pixels to three pixels on each horizontal scanningline can be accomplished by deriving an average pixel of two pixels ofthe horizontal scanning line and using the average pixel asinterpolation between the two pixels.

Assuming now that the primary color signal R inputted to the A/Dconversion circuit 22R has the SVGA form (800 by 600), each of thenumber of horizontal pixels and the number of vertical pixels isincreased to 1.25 times to generate a primary color signal R close tothe XGA form as shown in FIG. 5B. With respect to the primary colorsignal R supplied from the horizontal frequency conversion circuit 23R,four horizontal scanning lines are converted to five horizontal scanninglines by using the primary color signal R supplied from the line memory24R. Furthermore, in each horizontal scanning line, four pixels areconverted to five pixels. For converting four horizontal scanning linesto five horizontal scanning lines, one horizontal scanning line is takenin from the horizontal frequency conversion circuit 23R each time fourhorizontal scanning lines are taken in from the line memory 24R. The onehorizontal scanning line is disposed after the four horizontal scanninglines supplied from the line memory 24R.

Conversion of four pixels to five pixels is conducted by the followingmethod. Every four pixels, the last pixel of the four pixels is disposedagain to form five pixels. In other words, the last two pixels have thesame information contents. For further improving the precision, thegradation integral is used. As shown in FIG. 6A, the time range of fourpixels are virtually divided into five time regions and the amount ofdata in each time region is derived. As shown in FIG. 6B, each timeregion is adopted as a pixel having the derived data amount.

Such a gradation integral method can be used to convert the number ofpixels in the vertical direction by converting four horizontal scanninglines to five horizontal scanning lines. Whenever four horizontalscanning lines are taken in from the horizontal frequency conversioncircuit 23R or the line memory 24R in this case, each pixel is dividedinto time regions as shown in FIG. 6A with respect to each scanningline. For example, the time range of each pixel of the first scanningline is divided with a ratio of 4:1 to produce a first time range havinga proportion of 4/5 and a second time range having a proportion of 1/5.The preceding first time range having the proportion of 4/5 of eachpixel is adopted as a pixel having a data amount in the time range. Ascanning line formed by these pixels is adopted as the first horizontalscanning line after conversion. The time range of each pixel of thesecond scanning line is divided with a ratio of 3:2 to produce a thirdtime range having a proportion of 3/5 and a fourth time range having aproportion of 2/5. With respect to a corresponding pixel, the total ofthe second time range and the third time range is adopted as a pixelhaving a data amount of the total time range. A scanning line formed bythese pixels is adopted as a second scanning line after conversion.Thereafter, third, fourth and fifth horizontal scanning lines are formedin the same way. This method is very complicated. However, distortion ofdisplayed images can be sufficiently suppressed in conjunction with theconversion of the number of pixels in the horizontal direction usingthis gradation integral method for each horizontal scanning line.

When the primary color signal R inputted to the A/D conversion circuit22R has the XGA form, the horizontal frequency conversion circuit 23Rdoes not conduct the horizontal frequency conversion operation and thedisplay controller 25R does not conduct the pixel number conversion. Theprimary color signal R fed from the horizontal frequency conversioncircuit 23R or the line memory 24R is supplied to the display unit 7(FIG. 1) as it is. As shown in FIG. 5C, therefore, the image informationsignal having the XGA form supplied from the personal computer isdisplayed with its original number of pixels and display size.

As heretofore described, in this implementation form, a display unitcorresponding to the XGA having a sufficiently large number of pixelsand capable of displaying images of a high picture quality is used asthe display unit 7 such as a TFT liquid crystal panel. A received videosignal of a television program or an image information signal suppliedfrom a personal computer is converted to a signal of the XGA form anddisplayed on the display unit 7. Therefore, the image displayed by usingthe image information signal of the XGA form is displayed with itsgreatest possible picture quality without impairing the picture quality.Furthermore, the received video signal of a television program or animage information signal of the VGA or SVGA form supplied from apersonal computer is also displayed with a possible high picture qualityon the above described display unit 7.

Furthermore, in this implementation form, the video signal of the NTSCsystem is converted to the video signal of the VGA form. Therefore, sucha video signal can be processed as the output image information signalof the personal computer. The VGA-XGA conversion circuit can be usedcommonly for such a video signal as well.

While an implementation form of the present invention has heretoforebeen described, the present invention is not limited to such animplementation form.

For example, although the received television broadcast signal has beenassumed to be an NTSC system television signal, it may be a televisionsignal of another system. As for the image source, it is not limited totelevision broadcast signals or personal computers, but it may beanother image information signal. In this case as well, a display unitof high picture quality such as a liquid crystal panel corresponding tothe XGA is used and the image information signal of the image source isconverted to an image information signal of a system corresponding tothe display unit and then supplied to such a display unit.

In the above described implementation form, the video signal of thereceived television broadcast program is temporarily converted to animage information signal of the VGA form and then further converted toan image information signal of the XGA form. Alternatively, the videosignal of the received television broadcast program may be directlyconverted to an image information signal of the XGA form. In this case,this conversion unit is dedicated to this video signal and its outputand the output signal of the VGA-XGA conversion circuit 6 illustrated inFIG. 1 are switched and selectively supplied to the display unit 7.Furthermore, if a liquid crystal display device proposed by the presentinventors in JP-A-6-160878 is used as the display unit of the imagedisplay apparatus described in the implementation form, images of highdefinition can be displayed with a high visual field angle.

As heretofore described, the present invention makes it possible todisplay image information signals having different signal forms suppliedfrom image sources of different kinds as images by using the samedisplay unit, display images with a possible picture quality of thedisplay unit for any image information signal, and display images withapproximately equal high picture qualities irrespective of the kind ofthese image sources.

The present invention can be implemented in forms other than the abovedescribed embodiment without departing from the spirit or principalfeatures thereof. Therefore, the above described embodiment merelyexhibits an example of the present invention in every respect and itshould not be interpreted as restrictive. The scope of the presentinvention is defined by the claims. Variations and modificationsbelonging to the scope of the claims fall in the scope of the presentinvention.

We claim:
 1. An image display apparatus receiving, as inputs thereof, astandard television signal and a PC signal outputted from a personalcomputer and capable of displaying an image for each of said standardtelevision signal and PC signal, said image display apparatuscomprising:display means having a number of pixels larger than thenumber of pixels per screen of said PC signal and said televisionsignal; first signal conversion means for converting said inputtedstandard television signal to a signal format substantially equivalentto a signal format of said inputted PC signal; switch means forselecting and outputting either the signal outputted from said firstsignal conversion means or said inputted PC signal; and second signalconversion means for converting a number of pixels of an imageinformation signal outputted from said switch means to a signal having anumber of pixels substantially equivalent to the number of said displaymeans.
 2. An image display apparatus receiving as inputs a televisionsignal of the NTSC system and an image information signal having 640 by480 pixels and corresponding to the non-interlacing VGA standardoutputted from a personal computer and capable of displaying an imagefor each of said television signal and said image information signal,said image display apparatus comprising:display means having 1024 by 768pixels and corresponding to the non-interlacing XGA standard; anNTSC-VGA conversion circuit for converting said television signal to asignal having 640 by 480 pixels and corresponding to the non-interlacingVGA standard; switch means for selecting and outputting either thesignal outputted from said NTSC-VGA conversion circuit and said inputtedimage information signal; and a VGA-XGA conversion circuit forconverting a number of pixels of a signal outputted from said switchmeans to a number of pixels 1024 by 768 substantially equivalent to thenumber of said display means.
 3. An image display apparatus according toclaim 1, wherein said standard television signal is an NTSC systemsignal, and said PC signal is a non-interlacing VGA signal with 640 by480 pixels per screen.
 4. An image display apparatus according to claim1, wherein said standard television signal is an NTSC system signal, andsaid PC signal is a non-interlacing SVGA signal with 800 by 600 pixelsper screen.
 5. An image display apparatus according to claim 1, whereinsaid display means has a pixel number of 1024 by
 768. 6. An imagedisplay apparatus according to claim 1, wherein said display means has apixel number of 800 by
 600. 7. An image display apparatus according toclaim 1, wherein said first signal conversion means converts inputtedstandard television signals into a signal corresponding to anon-interlacing VGA signal with 640 by 480 pixels per screen.
 8. Animage display apparatus according to claim 1, wherein said first signalconversion means converts said inputted standard television signal intoa signal corresponding to a non-interlacing SVGA form with 800 by 600pixels per screen.
 9. An image display apparatus according to claim 1,wherein said second signal conversion means renders the number of pixelsper screen of signal to be supplied to said display means close to thenumber of pixels of said display means by multiplying the number ofpixels of each of the vertical and horizontal directions by 1.5 timeswhen the number of pixels per screen of signal outputted from saidswitch means for selecting is 640 by 480 and the number of pixels ofsaid display means is 1024 by
 768. 10. An image display apparatusaccording to claim 1, wherein said second signal conversion meansrenders the number of pixels per screen of signal to be supplied to saiddisplay means close to the number of pixels of said display means bymultiplying the number of pixels of each of the vertical and horizontaldirections by 1.25 times when the number of pixels per screen of signaloutputted from said switch means for selecting is 800 by 600 and thenumber of pixels of said display means is 1024 by 768.